Generally, a method of forming an image on the outside air is to use a water film, smoke, translucent artificial silk, mesh fabric, or the like as a medium onto which an image is projected.
With the water film or smoke among the aforementioned materials, the image is variable and not static. Accordingly, the image is uncontrollable, and sharpness and sustainment of the image are degraded.
The translucent artificial silk and mesh fabric block the rear view due to translucency thereof and significantly reduce sharpness and color due to low diffuse reflectance. Further, when they have a wide area for outdoor use, they cannot withstand the force of the wind (wind pressure).
A holographic screen having a hard transparent film, which is a type of transparent film for receiving a projected image, is most widely used for indoor holographic image projection.
FIG. 1 schematically illustrates configuration of a conventional holographic screen installed outdoors.
Referring to FIG. 1, the conventional holographic screen 10 is configured such that an image projected from an imaging device 11 is projected from behind a film-shaped transparent screen to display the image on the transparent screen.
Since the conventional holographic screen 10 causes an image to be projected onto a transparent film type screen, it secures transparency. However, since the conventional holographic screen 10 employs a method of forming an image by forming a thin film, it is used indoors or attached to a transparent plate in most cases. Therefore, when a large screen needs to be installed in an outdoor space, the conventional holographic screen cannot be used in reality due to the following problems.
First, since the conventional holographic screen 10 cannot withstand the wind, the screen alone cannot be installed outside.
Second, since the conventional holographic screen 10 reflects only a part of light due to transparency thereof, image quality is deteriorated, and sharpness and brightness are remarkably lower than those of a typical reflective screen.
Third, since the conventional holographic screen 10 is formed of a transparent hard film, it cannot be bent to have a desired shape.
The smooth surface of the holographic screen does not have a stereoscopic texture that causes diffuse reflection. To cause diffuse reflection to increase sharpness, foreign substances such as glass grains are attached to or inserted into the plate, or a net-shaped grid is printed on the plate or transparent yarn is attached to the plate.
Since these methods produce a plate-shaped structure and thus require high manufacturing costs, and the structure is heavy. Further, compared to a typical film-type holographic screen, the plate-shaped structure has reduced loss of sharpness, but requires higher production costs than the film type holographic screen.
In addition, in the case of the plate-shaped structure, diffuse reflection is insufficient and light scattering is weak because there is no air layer in the structure. Therefore, with the plate-shaped structure, sharpness is remarkably deteriorated compared to the image quality on a typical opaque reflective screen. Further, the plate-shaped structure is unsuitable for a large screen, and is restricted in size as it cannot withstand wind pressure when installed outdoors.
An opaque film reflective screen, which is popularized but is not a holographic screen, is also intended for indoor use and cannot withstand wind pressure, and thus it cannot be used outdoors when the size thereof is increased.
For these reasons, in order to realize a large screen for image projection in an outdoor space, the screen is basically required to withstand wind pressure and to have a large structure to support the screen while maintaining sharpness.
As imaging technology develops, activities such as outdoor advertisement and stage performances increasingly need large screens. Currently, however, most of the screens are not used for outdoor activities due to several problems including the above problems. Instead, a majority of large-scale images in outdoor spaces depend on LED display boards, which are costly due to heavy weight and installation complexity. Further, the structure blocks the rear view and thus deteriorates aesthetics of the city. In addition, it cannot be used for a holographic screen or the like.